Mechanistic insights into immune checkpoint inhibitor-related hypophysitis: a form of paraneoplastic syndrome.

BACKGROUND: Immune checkpoint inhibitors (ICIs) as a cancer immunotherapy have emerged as a treatment for multiple advanced cancer types. Because of enhanced immune responses, immune-related adverse events (irAEs), including endocrinopathies such as hypophysitis, have been associated with the use of ICIs. Most underlying mechanisms of ICI-related hypophysitis remain unclear, especially for programmed cell death-1 (PD-1)/PD-1 ligand 1 (PD-L1) inhibitors. We hypothesized that ICI-related hypophysitis is associated with paraneoplastic syndrome caused by ectopic expression of pituitary-specific antigens. METHODS: Twenty consecutive patients with ICI-related hypophysitis between 2017 and 2019 at Kobe University Hospital were retrospectively analyzed. Circulating anti-pituitary antibodies were detected using immunofluorescence staining and immunoblotting. Ectopic expression of pituitary autoantigens in tumor specimens was also examined. RESULTS: Eighteen patients were treated with PD-1/PD-L1 inhibitors, and two were treated with a combination of cytotoxic T-lymphocyte antigen-4 (CTLA-4) and PD-1 inhibitors. All patients showed adrenocorticotropic hormone (ACTH) deficiency and additionally, three showed thyroid-stimulating hormone (TSH) deficiency, and one showed gonadotropin-releasing hormone (GnRH) deficiency. Among these patients, three exhibited anti-pituitary antibodies, two with anti-corticotroph antibody and one with anti-somatotroph antibody. Interestingly, the anti-corticotroph antibody recognized proopiomelanocortin (POMC) and those two patients exhibited ectopic ACTH expression in the tumor, while the patients without anti-corticotroph antibody did not. CONCLUSIONS: We demonstrated 10% of PD-1/PD-L1 inhibitors-related hypophysitis were associated with the autoimmunity against corticotrophs and maybe caused as a form of paraneoplastic syndrome, in which ectopic expression of ACTH in the tumor was observed. It is also suggested that the pathophysiology is heterogenous in ICI-related hypophysitis.

Anti-pituitary antibodies against corticotrophs in IgG4-related hypophysitis.

PURPOSE: IgG4-related disease is a systemic inflammatory disease characterized by infiltration of IgG4-positive plasma cells into multiple organs, including the pituitary gland. Autoimmunity is thought to be involved in the pathogenesis of IgG4-related disease. The diagnosis of IgG4-related hypophysitis (IgG4-RH) is difficult because its clinical features, such as pituitary swelling and hypopituitarism, are similar to those of other pituitary diseases, including lymphocytic hypophysitis and sellar/suprasellar tumors. The presence and significance of anti-pituitary antibodies (APA) in IgG4-RH is unclear. METHODS: In this case-control study, we used single indirect immunofluorescence on human pituitary substrates to assess the prevalence of serum APA in 17 patients with IgG4-RH, 8 control patients with other pituitary diseases (lymphocytic infundibulo-neurohypophysitis, 3; craniopharyngioma, 2; germinoma, 3), and 9 healthy subjects. We further analyzed the endocrine cells targeted by the antibodies using double indirect immunofluorescence. RESULTS: APA were found in 5 of 17 patients with IgG4-RH (29%), and in none of the pituitary controls or healthy subjects. The endocrine cells targeted by the antibodies in the 5 IgG4-RH cases were exclusively corticotrophs. Antibodies were of the IgG1 subclass, rather than IgG4, in all 5 cases, suggesting that IgG4 is not directly involved in the pathogenesis. Finally, antibodies recognized pro-opiomelanocortin in 2 of the cases. CONCLUSIONS: Our study suggests that autoimmunity is involved in the pathogenesis of IgG4-RH and that corticotrophs are the main antigenic target, highlighting a possible new diagnostic marker for this condition.